[Enhancement] Supports altering column type / comment in SchemaChangeManager

[yuxiqian]

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Description

Currently, Schema change manager could apply CreateTable, AddColumn, DropColumn, RenameColumn events to Doris, but AlterColumnType / Comment aren't supported yet.

Solution

A new method alterColumnType / alterColumnComment could be implemented in SchemaChangeManager class by building corresponding DDL and reuse schemaChange method.

Are you willing to submit PR?

• [X] Yes I am willing to submit a PR!

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